Cumulative review

Science 9 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

Using the same 3.0 V battery, a student measures the current through nichrome wires of equal thickness: 10 cm, 0.60 A; 20 cm, 0.30 A; 30 cm, 0.20 A. Which conclusion do the data support?
1. a) The wire's length has no effect on its resistance
2. b) Longer wire has less resistance, so less current flows
3. c) The battery's voltage drops as the wire gets longer
4. d) Longer wire has more resistance, so less current flows
Students sampling a stream find many mayfly and stonefly nymphs. This most likely means the water
1. a) is polluted with sewage or fertilizer runoff
2. b) is too acidic for most other insects to live
3. c) is warm, still and low in dissolved oxygen
4. d) is clean and has plenty of dissolved oxygen
Two golden retriever puppies from the same litter have slightly different coat colours. This is an example of
1. a) variation between species
2. b) variation within a species
3. c) a change caused by the environment
4. d) two different species mixing
Which of these concentrations is equal to 1 ppm (one part per million)?
1. a) 1 mg in 1 kg
2. b) 1 g in 100 g
3. c) 1 mg in 1 g
4. d) 1 g in 1 kg
A chemical has an LD50 of 100 mg/kg when tested on dogs. For a 20 kg dog, what dose matches the LD50?
1. a) 2000 mg
2. b) 120 mg
3. c) 80 mg
4. d) 5 mg
A student drops identical antacid tablets into equal volumes of water at 10 °C, 25 °C and 40 °C and times how long each one fizzes. The manipulated variable is
1. a) the temperature of the water
2. b) the time the tablet fizzes
3. c) the volume of water used
4. d) the type of antacid tablet
A farmer cuts one high-yielding potato into pieces and plants each piece. The main advantage of this asexual method is that
1. a) the cut pieces mutate into plants that yield even more
2. b) each new plant gets genes from two different parents
3. c) the new plants will vary more, so some of them may resist disease
4. d) every new plant has the same genes as the high-yielding parent
A bacterium copies its DNA and splits into two identical cells. This type of reproduction is
1. a) sexual reproduction
2. b) budding
3. c) spore formation
4. d) binary fission
A lake next to farm fields turns bright green with algae in July. By August, many fish have died. Which explanation best fits?
1. a) The algae put so much oxygen into the water that the fish could not survive
2. b) Fertilizer runoff fed the algae; when they died, decomposers used up the oxygen
3. c) Fertilizer runoff poisoned the fish directly, and the algae grew on the remains
4. d) The extra nutrients made the lake water too basic for the fish to breathe
A farmer tests her field and finds the soil has a pH of 5. To raise the pH closer to 7, she should add
1. a) table salt, because salts are neutral
2. b) lime, a base, to neutralize some of the acid
3. c) a substance with a pH of 0 to balance it
4. d) vinegar, since adding an acid will cancel the acid

Answer key · Cumulative review

Science 9 · maddyhelps.com

d) Longer wire has more resistance, so less current flows — The voltage stayed at 3.0 V while the current fell, so the resistance rose: R = V ÷ I gives 5 Ω, 10 Ω and 15 Ω. Resistance grows with length, and at a fixed voltage more resistance always means less current.
d) is clean and has plenty of dissolved oxygen — Mayfly and stonefly nymphs need clean water with plenty of oxygen, so finding many of them is a sign of good water quality. Living things used this way are biological indicators, and they show the conditions over weeks, not just on the day of sampling.
b) variation within a species — Members of one species share the same basic features but differ in the details, and that is variation within a species. Variation between species is the bigger kind of difference, such as a dog compared with a cat.
a) 1 mg in 1 kg — A kilogram is a million milligrams, so 1 mg in 1 kg is one part in a million. For water, 1 kg is about 1 L, which is why 1 mg/L and 1 ppm are treated as the same; 1 g in 1 kg is a thousand times more concentrated.
a) 2000 mg — LD50 is given per kilogram of body mass, so multiply by the mass: 100 mg/kg × 20 kg = 2000 mg. Dividing 100 by 20 gives 5 mg, which would be the LD50 dose for an animal of only 0.05 kg.
a) the temperature of the water — The manipulated variable is the one the student deliberately changes, and here that is temperature. The fizzing time is the responding variable, which is measured; volume and tablet type are kept the same, so they are controlled variables.
d) every new plant has the same genes as the high-yielding parent — Asexual reproduction makes clones, so a good variety stays exactly as it is. More variation is the advantage of sexual reproduction, and the price of cloning is that one disease can strike every plant equally.
d) binary fission — Binary fission means splitting in two, and both new cells are identical to the parent. Budding is different: a small outgrowth forms on the parent, as in yeast, and breaks off later.
b) Fertilizer runoff fed the algae; when they died, decomposers used up the oxygen — Nitrogen and phosphorus from fertilizer let algae grow far faster than usual. When the algae die, bacteria decompose them and use up the dissolved oxygen, so the fish suffocate; the fertilizer never had to be toxic to kill them.
b) lime, a base, to neutralize some of the acid — A base neutralizes an acid and moves the pH up toward 7, and lime is what farmers spread on acidic soil. Adding salt does nothing to the acid: salt is a product of neutralization, not a cause of it.